These studies have focused on the regulatory properties of tyrosine hydroxylase, tryptophan hydroxylase, and their cofactor tetrahydrobiopterin (BH4) in the biosynthesis and release of catecholamine and serotonin in the brain. We have successfully cloned human brain tryptophan hydroxylase as a first step to characterizing its regulatory properties. We have purified the 14-3-3 protein from rat and bovine brains and investigated the role of 14-3-3 in the regulation of human recombinant tryptophan hydroxylase (fused with maltose binding protein) expressed in E.coli. Fusion tryptophan hydroxylase was phosphorylated in the presence of both cAMP-dependent protein kinase and calmodulin-dependent protein kinase II. Preliminary results indicate that the phosphorylated hydroxylase is activated by incubation with 14-3-3. Through the use of surface plasmon resonance spectroscopy, tight binding between 14-3-3 and tryptophan hydroxylase has been demonstrated.